Vertical rotary bipolar-type mercury process chlor-alkali electrolytic cell

ABSTRACT

A VERTICAL, CHLOR-ALKALI ELECTROLYTIC CELL IN WHICH MERCURY CATHODE SURFACES ARE VERTICALLY POSITIONED, EMPLOYING BIPOLAR ROTATABLE ELECTRODES DIVIDING THE CELL INTO A PLURAL NUMBER OF CELL CHAMBERS, WITH EACH CELL CHAMBER SEPA-   RATED FROM ADJACENT CELL CHAMBERS BY CURRENT CUT-OFF MEMBERS LOCATED ON THE CIRCUMFERENCE OF EACH BIPOLAR ELECTRODE.

March 14, 1972 o an YOKQTA EI'AL 3,649,508

VERTICAL ROTARY BIPOLAR-TYPE MERCURY PROCESS CHLOE-ALKALI ELECTROLYTIC CELL Filed Oct. 20. 1969 4 Sheets-Sheet l March 14, 1972 NORIYUKI YOKOTA EIAL 3,649,508

VERTICAL ROTARY BIPOLAR-TYPE MERCURY PROCESS CHLOR-ALKALI ELECTROLYTIC CELL 4 Sheets-Sheet 2 Filed Oct. 20. 1969 Gnu I H NORIYUKI YOKOTA H 5 VuHlIGAL ROTARY BIPOLAR-TYPE MERCURY PROCESS CHLOR-ALKALI ELECTROLYTIC CELL 4 Sheets-Sheet I 2 5 m 5 I H 1 k J J I y //////////////////////m V 6 l I. w I H \\\A\\\\ I .I

F F/V// a V March 14, 1972 Filed Oct. 20, 1969 QVHZ- March 14, 1972 NQRIYUKI YQKQTA ETAL 3,649,508

VERTICAL ROTARY BIPOLAR-TYPE CUBY PROCESS CHLOR-ALKALI ELECTROLY CELL 4 Sheets-Sheet 4.

Filed Oct. 20, 1969 3,649,508 VERTICAL ROTARY BIPOLAR-TYPE MERCURY PROCESS CHLOR-ALKALI ELECTROLYTIC CELL Noriyuki Yokota, Ashiya-shi, Shingo Tokuda, Nishinomiya-shi, and Shigeo Asada, Ibaraki-shi, Japan, assignors to Osaka Soda Co., Ltd., Osaka, Japan Filed Oct. 20, 1969, Ser. No. 867,611 Claims priority, application Japan, Oct. 22, 1968, 43/76,925 Int. Cl. C23b 5/68 US. Cl. 204-212 12 Claims ABSTRACT OF THE DISCLOSURE A vertical, chlor-alkali electrolytic cell in which mercury cathode surfaces are vertically positioned, employing bipolar rotatable electrodes dividing the cell into a plural number of cell chambers, with each cell chamber separated from adjacent cell chambers by current cut-off members located on the circumference of each bipolar electrode.

This invention relates to a vertical, rotatory bipolar-type mercury process chlor-alkali electrolytic cell using vertical mercury cathode surfaces, in which plural electrolytic chambers are compactly and horizontally disposed.

More particularly, the invention relates to a vertical, rotatory bipolar-type mercury process chlor-alkali electolytic cell, which comprises a bipolar rotatable body formed of a horizontal rotative shaft, plural bipolar discs coaxially fixed on said shaft at right angles with the axis line of said shaft but insulated from said shaft by an electrically insulative material, said discs being so disposed that the cathode and anode of any two adjacent bipolar discs are facing each other across a predetermined space, and electric current cut-off circular members extended along the circumference of each of said discs; a fixed cylindrical casing co-axially accommodating the rotatable body and forming plural, mutually independent electrolytic chambers together with the bipolar discs and current cut-off circular members; a cathode plate disposed in parallel with, and spaced from, one of the outermost discs, the outer side surface of which forms an anode plane and an anode plate disposed in parallel with, and spaced from, the other outermost disc of the outer side surface of which forms a cathode plane; outlet pipes for formed amalgam provided at the bottom of each of the electrolytic chambers; inlet pipes of saturated aqueous alkali chloride solution also provided at the bottom of each of said electrolytic chambers; and mercury feed pipes, formed chlorine gas outlet pipes, and depleted aqueous alkali chloride solution outlet pipes, all disposed at the upper part of each of said electrolytic chambers.

Horizontal or vertical mercury cathode electrolytic cells, for the electrolysis of solution of alkali metal salts, especially alkaline chlorides such as sodium chloride and the like are known, and various proposals have been made thereabout.

Normally in a vertical cell, the mercury cathode surface is vertically maintained, while it is horizontally disposed in a horizontal type cell. Also vertical and horizontal cells using monopolar electrodes and horizontal, non-rotative cell using bipolar electrodes are known. For example, a vertical, monopolar system electrolytic cell, in which the anode plate is fixed and cathode plate is rotated while one part thereof is immersed in mercury bath and the other, immersed in the bath of solution of alkali metal salts located on the mercury bath surface, is known from Japanese Pat. No. 160,750, and a similarly rotatable type horizontal, monopolar system electrolytic cell is known from US. Pat. No. 2,951,026, German Pat. No. 1,020,965; and US. Pat. No. 2,916,425.

United States Patent O Patented Mar. 14, 1972 The electrolytic cell of the subject invention is distinguished from the foregoing, in that it is a vertical cell in which mercury cathode surfaces are vertically positioned, employs bipolar electrodes, and is a rotatory type. In bipolar systems, the lead wires for connecting the plural anodes and plural cathodes, respectively, can be omitted, and therefore the cell srtucture can be markedly simplified in the absence of such lead wires and the facilities incidental thereto, compared with the known electrolytic cells employing monopolar electrodes. That is, with the bipolar system not only the electrical connection of each unit cell is simplified, but also the cell structure can be made more compact, and the floor area required therefor is advantageously reduced.

A bipolar electrode refers to such a plate, two sides of which serve each as anode and cathode. When it is used in mercury process alkali chloride electrolysis, the anode plane is formed of chlorine-resistant material, because chlorine ion are discharged from this plane, forming chlorine gas. Whereas, the cathode plane is formed by alkali amalgamating a metallic carrier which is easily Wettable with alkali amalgam. From this plane alkali metal ions are discharged to form amalgam.

As bipolar-type cells using such bipolar electrode, horizontal cells with non-rotative bipolar electrodes have been proposed, one of the very typical of which being disclosed in US. Patent No. 3,271,289.

The above patent teaches a bipolar types cell having a horizontal mercury cathode surface, in which plural horizontal unit electrolytic chambers are heaped up one on another in multiple stages. The advantages inherent in a bipolar system over the monopolar system are obtained, but because it is a horizontal cell, reduction in the amount of mercury required cannot be expected in a manner similar to horizontal, monopolar type cell. Furthermore, the lower unit electrolytic chambers must support the Weight of all unit electrolytic chamber thereabove. Thus the structure is subject to new restrictions as to strength, and the operational inconveniences are disadvantageously increased.

In order to overcome such drawbacks unavoidable with a horizontal cell as described above, we engaged in the development of a vertical bipolar type electrolytic cell.

We first attempted the experiment with vertical, plural unit electrolytic chambers divided by bipolar electrodes, whereby mercury is caused to flow down on the cathode planes of the bipolar plates, while electric current is passed through the unit electrolytic chambers via the bipolar plates. However, the described system was discovered to be disadvantageous in that (1) it is difficult to uniformly distribute and amalgamate the mercury over the carrier surface of the cathode plane, and if the carrier surface is partly exposed to the electrolytic solution, hydrogen ions are discharged instead of alkali metal ions, causing reduction in current efliciency; (2) the chlorine gas formed at the surfaces of anode planes of the bipolar electrodes facing to the cathode planes of the adjacent electrode at narrow intervals escapes and comes out to the solution surface with difliculty, and furthermore tends to non-uniformly adhere to the anode surfaces to cause localized differences in electric resistance, which in turn causes localized heat generation; and (3) the amount of chlorine gas formed at each unit anode surface is still increased particularly when current density is raised, so that the anode surfaces are incessantly covered by the chlorine gas to have poor contact with the electrolytic solution, which is one of the causes of rise in electrolytic voltage, thereby causing a very disadvanageous limitation on usable current density.

Furthermore, violent stirring of the electrolytic solution in each unit electrolytic chamber to eliminate the chlorine gas deposited on the anode surfaces gives rise to other disadvantages as to operation and apparatus.

It has now been discovered that the vertical, rotative bipolar-type system design as initially described very effectively overcomes the foregoing disadvantages inherent in monopolar system, those present in horizontal, nonrotative bipolar system, and the problems discovered in the above vertical, bipolar type system, and a very advantageous electrolytic cell can be provided.

Accordingly, the object of the present invention is to provide an improved electrolytic cell which is free from the various drawbacks in known monopolar and bipolar type mercury process alkali electrolytic cells. Still other objects and advantages of the invention will become apparent from the following descriptions.

Now referring to the attached drawings, FIGS. 1 and 2 show a typical embodiment of the cell in accordance with the invention, FIG. 1. being a plan view of the plate viewed from the direction of an end plate of the casing, with a part of the plate broken away, and FIG. 2 showing a longitudinal cross-section at line A-A' of FIG. I, viewed from the cylindrical side of the casing, with the central portion omitted.

FIG. 3 shows the cross-section similar to FIG. 2, showing a modification in the manner of cathode plate mounting, with the parts other than the vicinity of the cathode plate omitted.

FIG. 4a is a partial cross-sectional view showing the junction portion of the horizontal rotative shaft, on which the cathode plate of FIG. 2 is mounted, with the rotative shaft of lead rod, and FIG. 4b is a cross-sectional view thereof at line B-B' of FIG. 4a.

FIGS. 5a, 5b and 5c are partial cross-sectional views showing modifications of the current cut-off circular member, and FIG. 5:1 is a partial side view seen from the side of cathode plane of the bipolar plate of FIG. 5b.

In FIGS. 1, 2, and 3, the internal walls of the cylindrical casing 1 is coated with, or composed of, a chlorine-resistant, electrically insulative material such as rubber, synthetic resin, etc.

The bipolar rotor contained in the cylindrical casing 1 coaxially with the horizontal axis of the latter comprises a horizontal rotative shaft 2, plural bipolar discs 3, 3 which are coaxially fixed on the shaft 2 at right angles with the axial line of the latter, arranged in such a manner that between any two adjacent bipolar discs 3, 3, the cathode plane of the one is facing with the anode plane of the other across a fixed space, discs 3, 3 furthermore being insulated from the shaft 2 by an electrically insulative material, and current cut-off circular members 5, 5, 5 each extended along the circumference of each of discs 3, 3, 3

In this particular embodiment, the horizontal rotative shaft 2 and plural bipolar discs 3, 3, 3' are insulated from each other by the lining 4 of an electrically insulative material on the circumferential side of the shaft 2, through which the discs are fixed on shaft 2. As a useful insulative lining matedial, rubber, plastics, etc. may be named. If desired, shaft 2 may be formed of a thick, hollow pipe, and the whole shaft may be electrically insulated by an insulative lining over the entire surfaces thereof. Thus, the plural bipolar discs 3, 3, 3 are also mutually insulated.

The bipolar disc 3 can be formed, for example, by bonding an amalgam carrier metal 9, such as iron, nickel, and the like, with another metallic material 8 such as titanium, zirconium, tantalum, etc., and forming thereon a coating 7 of chlorine-resistant material, such as platinum, one of platinum group metals, or an alloy thereof, as clearly shown in the enlarged partial cross-section of FIG. 4a. Alternatively, the layer of metallic material 8 may be omitted, and the chlorine-resistant coating 7 may be directly applied onto one side of the amalgam carrier metal 9. The amalgam carrier metal side is alkali amalgamated to form the cathode plane, and the chlorine-resistant material-coated side provides the anode plane.

A plurality of such bipolar discs 3, 3, 3 are disposed in such a manner that the cathode plane and anode plane of any two adjacent discs should face each other across a suitable space or clearance. Consequently, one of the outermost discs has its anode plane facing outward, and the other has its cathode plane facing outward, that is, toward the respective end plate of the cylindrical casing 1. The number of discs and disc intervals can be suitably determined for each specific design.

The plural bipolar discs 3, 3, 3 each posses a current cut-olf circular member 5 extending along its circumference.

In FIGS. 1 and 2, particularly in FIG. 2, an embodiment is shown in which the peripheral portion of a current cut-ofll circular member 5 is rotatably extended between two circular members fixed on the internal wall of the cylindrical casing 1. The overlapping portions of the current cut-01f circular member 5 and two circular members on the internal wall of casing are rather closely positioned, while allowing the rotation of member 5 accompanying the rotation of shaft 2.

The current cut-01f circular member may have modified construction other than that illustrated in FIG. 2, only a few of such modifications being shown in FIGS. 5a, 5 b, and 5c.

In FIG. 5a, the current cut-off circular member is formed of two circular plates 5, 5, and the internal peripheral portion of a circular member fixed on the cylindrical wall of casing 1 is interposed therebetween with the clearances allowing the rotation of plates 5, 5. In FIG. 5 b, the outer periphery of the current cut-off circular member is extended to such an extent that it comes in contact with the internal wall of the cylindrical casing 1, while it is slidably rotatable in casing 1. Also two circular members 6', 6' are fixed on the internal wall, leaving a sufiicient space therebetween for the outer peripheral portion of the current cut-off circular member and formed amalgam outlet pipe 10. In such embodiment, the space between the members 6', 6' serves as a storage dam for leading the flowing-down amalgam to the outlet pipe 10, i.e., members 6, 6 serve as the flash-boards forming the dam, differently from the embodiments of FIG. 2 and FIG. 5a wherein the member or members form the current cut-01f portion together with the current cut-off circular members. The last embodiment can be further modified as illustrated in FIG. 50, wherein the outer peripheral portion of the current cut-off circular member is enlarged as shown by the cross-sectional view of FIG. 50, to assure the mutual independence of unit electrolytic chambers a a In the embodiments of FIGS. 5b and 5c, the members 6, 6 are not necessarily mounted all round the internal wall of the casing 1 in circular forms, but may be provided simply as two arc-formed fiashboards, as shown by partial side view of FIG. 5d which is the embodiment of FIG. 55 viewed from the direction of cathode plane 9. If desired, obviously it is permissible to employ circular members as shown in FIGS. 1 and 2, or in FIG. 5a.

The members 5, and 6', 6' are formed of rubber, synthetic resin, or of metallic plate coated with those chlorineresistant, electrically insulative materials.

Thus the current leakage between the unit electrolytic chambers a a a is cut off.

Furthermore, preferably between every two of the plural bipolar discs 3, 3, 3 a cylindrical spacer 17 is inserted to secure a fixed, predetermined distance between the adjacent bipolar discs.

The bipolar discs 3, 3, 3 can be fixed onto the rotative shaft 2 by various means. For example, the fixing may be effected by fixing keys 24, 24, as illustrated in FIG. 412. Or, circular depressions to be fitted with the discs may be formed in the insulative lining 4 or that and shaft 2. In both cases the spacers 17, 17, 17 assist to secure the fixing. The spacers can be formed of rubber,

synthetic resin, or of metals coated with such chlorine resistant, electrically insulative materials.

In the subject electrolytic cell, the bipolar rotor of above-described structure is rotatably and coaxially contained in a fixed cylindrical casing 1. The fixing of casing 1 can be readily effected by supporting the same with suitably provided arm, frame, feet, etc.

Thus, the plural bipolar discs 3, 3, 3 and current cut-ofi" circular members (optionally 5 and 6) form plural, mutually independent electrolytic chambers 0 a a a a a together with casing 1.

In the embodiment of FIG. 2, n1 sheets of bipolar discs are used to form n electrolytic chambers. In the drawing, facing with, and spaced from, the anode plane of the bipolar plate positioned at the extreme right, a cathode plate 11 is provided. Also facing with, and spaced from, the cathode plane of the bipolar plate positioned at the extreme left, an anode plate 12 is provided.

Said anode plate 12 and cathode plate 11 disposed in parallel with the bipolar discs are monopolar electrodes, which may be fixed or rotatably mounted. In FIG. 2, the anode plate 12 is fixed, and the cathode plate 11, on which the mercury or diluted amalgam supplied from the mercury feed pipe 13 flows down and spreads on the surface thereof, is made rotatable. That is, the anode plate is made of chlorine-resistant material, e.g. titanium, zirconium, or tantalum substrate coated with platinum, one of the platinum group metals, or an alloy thereof; or formed by the steps of bonding a metal such as copper, brass, iron, and the like with another metal material such as titanium, zirconium, tantalum, etc., and coating the same with platinum, one of platinum group metals, or an alloy thereof. The surfaces thereof except that facing with the cathode plane of the left end bipolar discs 3 are coated with a chlorine-resistant, electrically insulative material. The anode plate 12 is fixed on the internal wall of the end plate of easing 1, and the lead rod 12' thereof is protruding out of the casing 1, piercing through the end plate. The lead rod 12' is electrically connected to the anode of a power supply (not shown). Since the internal surface of the end plate is formed of an insulative material, the end plate and the anode plate 12 are insulated from each other.

The anode plate is shown as a sheet of circular (or doughnut) plate in FIG. 2, but it is also possible to divide it into several radical pieces from the center thereof, and mount them in such a manner that they as a whole form a circular plate.

Also the rotatable cathode plate 11 of FIG. 2 can be subject to such a design change as shown in FIG. 3, wherein a cathode lead rod 11 is projected outside the casing 1, piercing through the end plate of casing 1 similarly to the case of anode plate.

When the cathode plate 11 is thus fixed, there occurs a tendency that the mercury or dilute amalgam, which is supplied onto the surface of cathode plate 11 from the mercury feed pipe 13 and flows down on the surface, fails to uniformly spread on the surface. The tendency can be preferably prevented by provision of a known mercury distributor below the mercury feed pipe 13. When the cathode plate 11 is rotatable as described hereinbelow, such mercury distributor is unnecessary.

A rotatable type cathode plate is shown in FIG. 2, which is electrically connected to the end of horizontal rotative shaft, at the portion contacting with the rotative shaft 2 which also serves as a cathode lead rod. The plane of plate 11 facing against the end plate is covered with an electrically insulative sheet 15 which is coaxially joined with the rotative shaft 2'. The joining of shafts 2 and 2' can be effected, for example, by providing a projection 2" on the joining side of shaft 2', the projection 2" and a hole fitting therewith which is bored on the shaft 2 being cut respectively with screw threads and screw grooves, as shown in the enlarged cross-section of FIG. 4a. If desired,

6 such other means as inserting, soldering, etc. can be utilized.

The shafts 2 and 2' are thus joined while interposing the cathode plate in fixed state therebetween, as a whole forming an integrated rotative shaft, i.e. the three members can rotate synchronously.

The rotative shaft 2' which serves also as the cathode lead rod is suitably formed of an electrically conductive material, such as copper, brass, etc. The shaft may be reinforced with such core material as iron, steel, etc. to be given an increased length. Alternatively, plural copper lead rods may be buried in an iron or steel shaft in the position corresponding to the contact portion of cathode plate 11 and shaft 2, referring to FIG. 4a, in such a manner that ends of the rods conductively contact with the cathode plate 11. Whereby the strength of the shaft 2' can be markedly increased, allowing the same to serve also as a cathode lead rod.

lIn the latter case, the other ends of the copper lead rods buried in the shaft 2' may be contacted with, for example, a copper circular belt, so that they may come in slidable contact with the sliding cathode connector 16 shown in FIG. 2, the circular belt appearing on the surface of the portion where the shaft 2 contacts with the connector 16. It is also possible to make the circumferential sides of the lead rods insulative with an electrically insulative material before the burial.

The foregoing description of rotatable mounting is given as to cathode plate, but it is perfectly applicable also to rotatable mounting of anode plate.

When both anode and cathode plates are rotatably mounted, their faces coming into contact with the shaft 2 are electrically insulated, so as to prevent shorting between the two poles through shaft 2. In that case, it is a preferred practice to join the two shafts 2 and 2' by inserting as shaft 2 a thick, hollow tubular shaft with its entire internal and external surfaces lined with an insulating material. Obviously, it is desirable that when the cathode plate alone is made rotatable as illustrated in FIG. 2, the contacting faces of the two shafts should be insulated through an insulating material, although such is not essential and not shown.

In FIGS. 1 and 2, the casing 1 is shown as a cylindrical body with two end plates attached to its right and left ends by bolting up the nuts 14, 14 (In FIG. 2, each nut is shown at the top and bottom, indication of other nuts being omitted.) But as can be readily understood, various design modifications are prefectly permissible. For example, the casing 1 can be formed of two semi-cylindrical members by dividing a cylindrical casing with a horizontal plane passing through the horizontal axis of the cylinder, so that the casing can be freely opened and closed, although designed water-tight. In such a case, if the anode plate and/or cathode plate is mounted in fixed manner, the plate should be divided into plural, i.e., at least 2, pieces, so that when the casing is opened, the plate can be separated accompanying each the semicircular end plate of semi-cylindrical member.

Further referring to FIG. 1, 14' denotes a bolt hole. Also in FIGS. 1 and 2, 18, 18 denote bearings rotatably supporting the rotative shaft 2; 19, 19 are the stuffing boxes to seal the contacting and rotating portion of the roative shaft 2 with casing 1; and 20, 20 are packings thereof.

In the subject electrolytic cell, at the bottom of each of the unit electrolytic chambers thus formed, a formed amalgam outlet pipe 10 and a saturated aqueous alkali chloride solution inlet pipe 21 are disposed. (Each is shown in FIG. 1 but omitted from FIGS. 2 and 3.)

Furthermore, each unit electrolytic chamber is provided with, at its upper part, a mercury feed pipe 13, formed chloride gas outlet pipe 22, and dilute aqueous alkali chloride solution outlet pipe 23 (each is shown in FIG. 1 but omitted from FIGS. 2 and 3).

An example of electrolytic operation using the verticaltype, rotatory bipolar system mercury process chlor-alkali electrolytic cell as illustrated in FIGS. 1 and 2 will be described hereinbelow, in which sodium chloride is used as an alkali chloride. Obviously, potassium chloride can be electrolyzed in quite similar manner.

Referring to FIGS. 1 and 2, the rotative shaft 2 and rotative shaft 2' joined thereto and which serves also as the cathode lead rod are integrally driven and rotated (the driving mechanism is not shown) causing the plural bipolar discs 3, 3, 3 forming mutually independent, plural unit electrolytic chambers a a a a to rotate in the casing 1. Mercury or dilute amalgam (that obtained through denuder) is fed through the mercury feed pipe 13 on the upper part of each unit electrolytic chamber, onto the cathode plane 9 of the bipolar disc 3 and the surface of cathode plate 11, which is spread on the entire cathode plane as a uniform, thin flowing film, assisted by the rotating motion of the cathode plate.

Separately, saturated aqueous sodium chloride solution is fed into each electrolytic chamber from the inlet pipe 21 provided near the bottom of each chamber.

The rotative shaft 2' is connected to the cathode bus bar through sliding cathode connector 16, and the anode lead rods 12', 12" 12" are connected to anode bus bar. Upon supplying of electric current, each right side surface of the bipolar disc 3 functions as an anode, and the left side surface fuctions as a cathode, and electrolysis is conducted in each unit electrolytic chamber.

From the surfaces of the cathode plate and cathode planes of the bipolar discs, sodium ion is discharged, to convert the mercury flowing down on the surfaces as uniformly spread thin film to sodium amalgam. If dilute sodium amalgam is used in place of mercury, its concentration is increased by the sodium ion discharge. The formed amalgam flowing down on the surfaces is collected at the bottom of each unit electrolytic chamber, and withdrawn through the outlet pipe provided in each of the chambers, continuously at a suitable rate. The withdrawn sodium amalgam from chamber is each electrically insulated, and thereafter normally collected into a single passage and led to a well known, suitable amalgam decomposer. Alternatively, when such advance insulation is not effected, a decomposer is connected to each of the outlet pipes 10 to decompose the amalgam to mercury or dilute amalgam. The mercury or dilute amalgam is recycled into the system through mercury feed pipe 13 of each electrolytic chamber. Also the liquid caustic soda formed in the decomposer is either used as a finished product as it is, or concentrated in the accepted manner.

Whereas, on the surfaces of anode plate 12 and anode planes of bipolar discs 3, 3, 3 chlorine ion is discharged to form chlorine gas, which is readily removed from the anode surfaces as assisted by the rotating motion of the anode plate, withdrawn from the outlet pipe 22 provided in each chamber at the upper part of the casing 1, and normally collected into single passage to serve as, for example, hydrochloric acid synthesizing material, or chlorine gas source of other industries as it is. Although not shown, it can be readily understood that the openings of the chlorine gas outlet pipes in the casing should be located higher than the openings of dilute aqueous sodium chloride solution outlet pipes 23 in the casing, the solution being formed as the sodium chloride in the saturated solution is consumed 'by the electrolysis.

It is normally preferred to select such operating conditions that the sodium amalgam level at the bottom of each unit electrolytic chamber should reach the opening of the outlet pipe 10 in the casing. The position of opening of the starting saturated aqueous sodium chloride solution supply pipe in the casing is suitably selected between the bipolar disc and mercury outlet pipe. Also the position of the dilute aqueous sodium chloride solution outlet pipe in the casin is suitably within the range a little above the upper end of bipolar disc to below the mercury feed pipe.

The dilute saline water withdrawn from the outlet pipe 23 is recycled to the preparation step of starting saturated sodium chloride solution, in accordance with the conventional practice.

In the foregoing, an example of practicing the electrolysis by rotating the bipolar rotor has been explained. It is also possible to operate the subject apparatus by swinging the rotor axis as illustrated in FIG. 2 back and forth, with the section shown in FIG. 2 at the center. The preferred angle of swinging is at least In the subject vertical, rotatory bipolar type mercury process chlor-alkali electrolysis cell, the spreading of mercury on the cathode planes can be effected very uniformly in the form of thin film over the entire cathode surfaces. Therefore, even when the manner of mercury flow is varied during the operation, there is no danger of the cathode plane being exposed or the film thickness becoming uneven. Thus the amount of mercury required can be reduced, and with less mercury amount stable electrolytic operation can be performed. Furthermore, current efficiency is improved, and operationally disadvantageous variation of current efficiency can be avoided. Also because the anode planes of bipolar discs rotate synchronously, the chlorine gas formed and deposited on the planes can be readily and effectively removed, always securing good contact of the surfaces with electrolytic solution. Thus the rise in electrolytic voltage due to the deposition of fine bubbles of chlorine gas on anode planes and objectionable voltage variation can be prevented, allowing constant, stable electrolytic operation.

Furthermore, since the wear of anode plane due to oxidation occurs evenly, local exposure of substrate (e.g. iron or titanium plate 9 or 8) caused by localized wear of chlorineresistant coating (e.g., platinum coating 7) can be prevented, and the distance between any two ad jacent anode and cathode planes can be maintained constant. In this respect also the objectionable rise and variation in electrolytic voltage can be advantageously inhibited.

Still in addition, the cell has very compact structure and requires economically reduced floor areas, nevertheless exhibiting high electrolytic processing capacity. The cell is furthermore free of all defects present in the already described, known monopolar and bipolar type electrolytic cells.

EXAMPLE 1 An electrolytic cell in accordance with the invention was manufactured with five bipolar discs of 40 cm. in diameter and 10 dm. in total anode plane area forming six electrolytic chambers. The cell was operated under below-specified conditions:

Electrolytic current-500 a.

Current density50 a./dm.

Rotation rate of electrode-30 rotations/ min.

Concentration of sodium chloride solution supplied- 300 g./ liter Sodium chloride solution supplied40 liters/ hr. chamber Mercury supplied-12 liters/hr. chamber The resulting cell voltage was 23.1 volts, flowing amalgam concentration was approximately 0.25%, and over-all current efiiciency was 97%.

EXAMPLE 2 The operation of Example 1 was repeated except that the bipolar discs were caused to swing by 90 instead of being rotated. The current efficiency was We claim:

1. A vertical, rotatory bipolar system mercury process chlor-alkali electrolytic cell, which comprises a bipolar rotatable body formed of a horizontal rotative shaft, plural bipolar discs coaxially fixed on said shaft at right angles with the axis line of said shaft but insulated from said shaft with an electrically insulative material, said discs being so disposed that the cathode and anode of any two adjacent bipolar discs are facing each other across a predetermined space, and electric current cut-off circular members extended along the circumference of each of said discs; a fixed cylindrical casing having two end plates coaxially accommodating the rotatable body and forming plural, mutually independent electrolytic chambers together with said bipolar discs and current cut-off circular members; a cathode plate disposed in parallel with, and spaced from, one of the outermost discs, the outer side surface of which forms an anode plane, and an anode plate disposed in parallel with, and spaced from, the other outermost disc, the outer side surface of which forms a cathode plane; outlet pipes for formed amalgam provided at the bottom of each of said electrolytic chambers; inlet pipes for saturated aqueous alkali chloride solution provided at the bottom of each of said electrolytic chambers; and mercury feed pipes, formed chlorine gas outlet pipes, and depleted aqueous alkali chloride solution outlet pipes, disposed at the upper part of each of said electrolytic chambers.

2. The cell of claim 1, wherein said anode plate is fixed on the internal wall of one of said two end plates of said casing, and the lead rod of said anode plate is projecting out of said casing, piercing through said end plate.

3. The cell of claim 1, wherein said anode plate is supported by and electrically connected to a rotative shaft, one end of said rotative shaft serving as a lead rod, at the portion of connection with said anode plate.

4. The cell of claim 1, wherein the outer peripheral portion of each current cut-oif circular member is rotatably extended between two circular members fixed on the internal wall of the cylindrical body of said casing.

5. The cell of claim 1, wherein each of said current cut-E circular members is formed of two circular plates, and between said plates the internal peripheral portion of a circular member fixed on the internal Wall of the cylindrical body of said casing is rotatably extended.

6. The cell of claim 1, wherein the outer peripheral portion of each current cut-off circular member is extended until it comes into slidable contact with the internal wall of the cylindrical body of said casing, and on said wall of said casing two circular members are fixed at such relative positions forming a space for said peripheral portion and formed amalgam outlet pipe therebetween.

7. The cell of claim 1, wherein the outer peripheral portion of each current cut-off circular member is extended until it comes into slidable contact with the internal wall of the cylindrical body of said casing, and two arcformed plates are fixed on the internal wall at such relative positions leaving a space for said outer peripheral portion and formed amalgam outlet pipe therebetween.

8. The cell of claim 1, wherein the circumferential side of the horizontal rotative shaft is coated with an electrically insulattive material.

9. The cell of claim 1, wherein the cathode plane of each bipolar disc is formed of an amalgam carrier metal selected from the group consisting of iron and nickel, and the anode plane is formed of a substrate of a metal selected from the group consisting of titanium, zirconium, and tantalum, coated with a chlorine-resistant material selected from the group consisting of platinum, platinum group metals, and alloys thereof.

10. The cell of claim 1, wherein said cathode plate is fixed on the internal wall of one of said two end plates of said casing, and the lead rod of said cathode plate is projecting out of said casing, piercing through said end plate.

11. The cell of claim 1, wherein said cathode plate is supported by and electrically connected to a rotative shaft, one end of said rotative shaft serving as a lead rod, at the portion of connection with said cathode plate.

12. The cell of claim 1, wherein the cathode plane of each bipolar disc is formed of an amalgam carrier metal from the group consisting of iron and nickel, and the anode plane is formed of an amalgam carrier metal from the group consisting of iron and nickel directly coated with a chlorine-resistant material selected from the group consisting of platinum, platinum group metals, and alloys thereof.

References Cited UNITED STATES PATENTS 6/1958 Vellas et al. 204-212 4/1969 Colman 204-268 U.S. Cl. X.R. 204-99, 268 

